Targeting cells involved in angiogenesis cripples rapidly growing tumors by limiting the oxygen and nutrients supply or, depending on the strategy employed, increasing the susceptibility of tumor cells to chemotherapy by enhancing the efficiency of a delivered drug via vascular network reorganization. Resistance of tumor cells to anti-angiogenesis treatment has been observed in mouse systems and reported for human studies for several different treatments. Additionally, the tumor microenvironment (TME) recruits myeloid-derived suppressor cells (MDSC) that are responsible for the necessary angiogenic switch needed for tumor growth and eventual dissemination.
Studies performed by several investigators have repeatedly shown the importance of targeting tumor angiogenesis because of its central role in invasion, growth, and metastasis. Since tumor cells frequently mutate in response to therapy or downregulate MHC class I molecules required for T cell-mediated responses, targeting endothelial cells and pericytes, which are essential for tumor survival and may lack the immunosuppressive mechanisms deployed by tumors, would be advantageous.
However, thirty years after angiogenesis was shown to play an enabling role in cancer, modern medicine is still trying to develop novel compounds and therapeutics to target the tumor vasculature. However, most therapeutics require multiple rounds of administration and can have toxic side effects.